Electrodeposition of neptunium



Aug. 30, 1960 G. T. sEABoRG ETAL 2,951,013

ELECTRODEPCSITION 0F NEPTUNIUM Filed Oct. 29, 1945 F`lE-1 Gle/zz?7.15.5605 0129,

ELECTRODEPOSITION F NEPTUNIUM Glenn T. Seaborg, Chicago, Ill., andArthur C. Wahl, Santa Fe, N. Mex., assignors to the United States ofAmerica as represented by the United States Atomic Energy CommissionFiled Oct. 29, 1945, Ser. No. 625,136

1 Claim. (Cl. 21M-1.5)

This invention relates to a method of separating certain new elementsfrom solutions. More particularly it perrains to a process involving theelectrolytic deposition of neptunium from solutions thereof.

It is known that plutonium can be produced in small quantities by thebombardment of natural uranium with neutrons. The designation plutoniumor element 94 as used throughout the present description refers to thetransuranic element having an atomic number of 94. The expression 94239means the isotope of element 94 has an atomic weight or mass of 239.Similarly, the terms element 93 or Np refer to the new element known asneptunium having an atomic number of 93.

Uranium is composed of three isotopes, namely, U234, U235 and U238, thelatter being present in excess of 99 percent of the whole. When U238 issubjected to the action of slow or 4thermal neutrons, a fourth isotope,U239, is produced having a half-life of 23 minutes-and undergoes betadecay to Np239 which decays further by beta radiation with a halflife of2.3 days to yield plutonium. In addition to the formation of thetransuranic elements, neptunium and plutonium, there are simultaneouslyproduced other elements of lower atomic weight known as fissionfragments. These fission fragments are composed of two distinct elementgroups, i.e., `a light and heavy element group. The light group containselements having atomic numbers of between about 35 and 46 while theheavier group is composed of elements of atomic numbers varying betweenabout 5l and 60. The elements of these groups as originally produced areconsiderably overmassed and undercharged, :and hence are highlyunstable. By beta radiation, however, they quickly transform themselvesinto isotopes of these various elements having longer half-lives. Thelresulting materials are commonly known as fission products. It isparticularly desirable to separate the neptunium and plutonium from theradio` active fission fragments and fission products thereby removingfrom the mass, subjected to neutron bombardment, the radioactivematerials and particularly the light elements such as the Alight metalshaving very short halflives. Y

It is= 'an object of this invention to provide ra simple and e'icientmeans of separating neptunium from solutions and particularly carryingout this separation in a quantitative manner.

It is a further object of this invention to accomplish this result byelectrolytic means without the use of added reagents and without thenecessity of evaporating the solution to dryness.

Another object of the present invention is to provide a simple, rapid,and eicient means for producing a thin ilm of neptunium.

Further objects will be apparent from the accompanying drawing and thedescription which follows.

Subsequent to the bombardment of uranium with neutrons to produce newelements a's discussed above, the usual procedure is to dissolve theentire mass in a suitable acid, such as nitric acid. This solutioncontains uranium, neptunium, plutonium, and all of the other productsresulting from the fission of U23?.

In view of the relatively short half-life of neptunium, it is importantthat any method of separation of this element employed be a rapid oneinvolving a minimum consumption of time.

In the study of radioactive substancessuch as neptunium, it is often ofgreat importance to obtain a very thin uniform layer of the substance inquestion so that its radioactivity can be measured. If the layer is toothick there will be self-absorption phenomena that will seriouslyinterfere with radioactivity measurements.

In accordance with the present invention it has been found thatneptunium may be recovered by electrodeposition from solutions thereof.Nonaqueous solutions of neptunitun such as, solutions of neptuniumnitrate in absolute ethyl alcohol or other organic solvent capable ofsupplying a pair of electrons to neptunium'to ,form a coordinate linkagesuch as, acetone, methyl ethyl ketone, hexone, methanol, n-propanol,ethyl ether, cellosolve, formamid, acetamid, acetic acid or other-solvent containing the group C=O, -N=, -S-, etc., may be used for thispurpose.

The aqueous solutions from which neptunium is deposited may vary widelyin their hydrogen ion concentration; however, in the majority ofinstances it is generally preferable to employ a pH of between about 5and 7. Suitable buffers such as acetic acid-sodium acetate, carbondioxidesodium bicarbonate buffers, etc. may be used to establish thedesired pH.

The process 'of the present invention may be carried out in any standardelectrolytic apparatus. A suitable apparatus is shown in Fig. l whereinthe electrolyte 1 is contained in a glass cylinder 2 having a silverbottom 3 connected to lead lline 4 which is in turn connected to anegative source of potential. Anode 5 and cathode 3 consist of platinum`or insoluble anode material and silver, respectively and are connectedto a suitable source of direct current such as a battery. The connectionis made through switches 6 and 7 and variable resistance 8. In order ltomeasure the amount of current used a milliammeter 9 with a switchconnection 10 for low and high scale readings, is placed in the line. Inorder to measure the voltage with a Very small current loss amicroammeter 11 is placed across the line and in series with two fixedhigh resistances 12 and 13. As actually used resistance 12 is 0.1 megohmand resistance 13 is 1.0 megohm.

When using 4the apparatus the electrolyte consists preferably ofneptunium nitrate and lanthanum nitrate in absolute alcohol. The currentis passed through the solution and the amperage is adjusted by means ofthe vari.- yable resistance 8.

It was found that when carrying out such an electrolysis the famp'eragerises continuously with time as shown in Fig. 2.

In effecting the process of the present invention a relatively widevoltage range may be utilized. For themajority of instances, however,voltage of between about 2 and 50 volts have been found adequate fornonaqueous electrolytes and for aqueous medium a somewhat lower voltage,e.g. 2 to about l() volts, is suitable. Likewise, the current densitiesused may cover a comparatively wide range, however, for most purposes ithas been found entirely satisfactory to use current densities of betweenabout 0.001 and 0.6 ampere per square decimeter. The temperaturesemployed may, in general, vary from `about.

` 30 C. to about 90 C.

The process of the present invention may be further illustrated byreference to the following specific examples.

In all instances the percentages of neptunium plated out was determinedin the manner referred to in Example 1.

Example 1 K thus obtained was again dissolved in nitric acid',evaporated to dryness on asteam bath, andy dissolved in absolutealcohol. The precipitate did not entirely dissolve and the solution Wasltered and diluted to cubic centimeters With absolute alcohol. Thesolution was centriuged to remove the small amount of precipitate stillremaining.

Two cubic centimeters of this solution of neptunium nitrate andlanthanum nitrate in absolute alcohol was electrolyzed in an apparatussimilar to that illustrated in Fig. 1. The electrolysis was carried eutfor forty-live minutes at 510 volts. The current density varied over thetime of electrolysis from 1.8 to 4.7 milliamperes per square decimeteras shown in the curve of Figure 2. The electrodeposited neptunium waswashed with absolute alcohol. On the basis of determinations of betaradiation from aliquot portions of the initial neptunium solution andthe electrolyte after the plating operation, using standard counter tubetechniques, it was found that 100 percent of the neptunium in solutionwas deposited on the cathode probably in the form of an oxide.

Example 2 One cubic centimeter of the solution prepared as described inExample 1, was mixed with 1 cubic centimeter of a solution of lanthanumnitrate in absolute alcohol. The resulting solution was electrolyzedusing the apparatus shown in Fig. 1. The electrolysis was carried outfor thirty-five minutes at 17 volts and a current density of 3 to 5milliamperes per square decimeter. Forty-eight percent of the neptuniumwas plated out. With 2 cubic centimeters of the electrolyte described inExample l, 8l percent of the neptunium was plated out, using a voltageof between 20 and 40 volts and a current of 2-4 milliamperes per squaredecimeter vfor a period orfY fifteen minutes.

Example 3 A solution of a `small quantity of neptunium prepared tive.

last traces of lanthanum carrier were removed from the neptunium in theprocess of separating that element from the nitric acid solution ofneutron bombarded uranium.

Example 4 A solution containing a small amount of neptunium in one molalammonium acetate solution was electrolyzed for ftyrninutes. The currentdensity was 0.15 ampere per square decimeter, `at a voltage of from-2.4to 2.7. The temperature was maintained at from 79 to 84 C. Seventy-fourpercent ofthe neptunium was removed from this solution probably in theform of oxide.

Examplev 5 An aqueous molal ammonium acetater solution containing .01mole 4of uranyl ion (UO2-l-}-) and a tracer quality of neptunium wassubjected to electrolysis at a current density of 0.15 ampere. persquare decimeter and at a voltage of from about 2.4 to 2.7 volts. Thetemperature of the solution was maintained at from Iabout 79 to 84 C.The electrolysis was carried out for about sixty-live minutes, at theend of which time 97 percent of the neptunium, probably as an oxide, and98 percent of the uranium had been removed from the solution.

It is to be Istrictly understood that the foregoing examples are merelyillustrative and yare in no Way limita- It will be apparent to thoseskilled in the art that the present invention is susceptible of numerousimprovements and modifications without departing from the scope thereof.For example, the current density employed may be substantially higherthan speciiied in the foregoing description merely by using a rotatingcathode, increasing the rate of agitation, or altering the bathtemperature. In general, it may be said that any procedure for therecovery of neptunium based upon the electrolytic deposition thereoffrom its solution is to be regarded as lying within the scope of thisinvention.

What is claimed is:

The process of electrodepositing neptunium from solutions thereof, Whichcomprises conducting the electrodeposition from Ian absolute alcoholbath containing a neptunium nitrate and lanthanum nitrate at a potentialof approximately fifty volts and a current density of between labout 1.8and 4.7 milliarnperes per square decimeter.

References Cited in the tile of this patent UNITED STATES PATENTS MeyerNov. 3, 1908 Dennis Nov. '3, 1914 OTHER REFERENCES Uranium and AtomicPower by] ack De Ment and H. C. Dake, published by Chemical PublishingCo., Brookyln, New York, 1941, pages 72, 123, 124, 184.

The Heavy Elements, Chem. Eng. News, 24, pages 1193-1198, May 10, 1946.

Plutonium and Other Transuranium Elements, Chem. Eng. News, 25, pages358-60, 397, Feb. 10, 1947.

